Fuel used as the power source for vehicle engines is susceptible to being contaminated by sand, dirt and other particulate materials. Fuel also is susceptible of being contaminated by water. Because of these problems, most vehicles use a fuel filter prior to delivering the fuel to the fuel distribution device, whether it be a carburetor or a fuel injection means. Fuel which has been contaminated by water will not function properly in a vehicle engine. This is particularly true of diesel fuel. Diesel engines use fuel injection as the primary means of delivering the fuel to the engine. Fuel injection systems use injectors which have extremely small bores and are susceptible to plugging by particulate material. Diesel fuel becomes more viscous as the temperature is lowered. It is therefore not uncommon to heat a fuel filter used with a diesel engine.
One method of heating a fuel filter is by circulating water from the engine block either through or around the fuel filter. This method of heating a filter causes two problems. External water lines must be used which can increase the potential of leaks in the engine cooling system and freezing of the external lines. The second problem is that a leak of the water line could introduce water into the fuel contaminating the fuel.
The present invention overcomes these problems by using excess fuel from the fuel injection system which is normally routed back to the fuel tank. This excess return fuel has been warmed by the engine manifold. The preheated return fuel is circulated through heat exchanger inside the fuel filter to heat the filtered fuel before the excess fuel returns to the fuel tank.
In addition to eliminating the problems described above, it has been found that vehicles equipped with this heated fuel filter have improved fuel mileage of 3/4 miles per gallon. Particulate emissions, or smoke, is also reduced by preheating the fuel. Excessive heating of the fuel in the fuel tank is also reduced.